The present invention relates to a method and an apparatus for measuring the temperature of substrates, in particular semiconductor substrates or wafers, with at least one radiation detector for measuring the radiation emitted by the substrate, and an element that restricts the field of vision of the radiation detector and that is arranged between the substrate and the radiation detector. The invention furthermore relates to an apparatus for measuring an object temperature of an object, with at least one heating apparatus including at least one heating element for heating the object by means of electromagnetic radiation, with at least one first radiation detector that detects the radiation coming from the object within a first field of vision.
The invention described in greater detail in the following is used advantageously in so-called RTP (rapid thermal processor) systems in which wafers undergo thermal processing. RTP systems and the rapid heating process used in these systems are known from publications DE 4 437 361 C, DE 4 012 615 C, DE 4 223 133 C, or D 4 41 439 1A, as well as from U.S. Pat. Nos. 5,226,732, 5,359,693, and 5,628,564. Additional rapid heating processes and apparatus are described in the following publications: J. Nackos: 2nd International Rapid Thermal Conference, RTP '94. Monterey Calif., Proc. p. 421-428 (1994); Arun K. Nanda, Terrence J. Riley, G. Miner et. al.: “Evaluation of Applied Materials Rapid Thermal Processor Using SEMATECH Metrologies for 0.25 μm Technology Thermal Applications” Part II, Presentation at the Rapid Thermal and Integrated Processing Conference MRS Spring Meeting '96, San Francisco Calif.; Terrence F. Riley, Arun K. Nandam, G. Miner, et. al.: “Evaluation of Applied Materials Rapid Thermal Processor Using SEMATECH Methodologies for 0.25 μm Technology Thermal Applications” Part I, ibid; R. Bremsensdorfer, S. Marcus, and Z. Nenyei: “Patterns Related Nonuniformities During Rapid Thermal Processing”, presentation at the Rapid Thermal and Integrated Processing Conference MRS Spring Meeting '96, San Francisco Calif., and subsequently published document by Z. Nenyei, G. Wein, W. Lerch, C. Grunwald, J. Gelpey, and S. Wallmüller: “RTP Development Requirements”, presented at RTP '97 Conference Sep. 3-5, 1997 New Orleans. In all of these methods it is necessary to measure the temperature at at least one point or surface section of the object, substrate, or wafer, or the entire substrate surface during the thermal processing procedure. In general, provided for temperature measurement is at least one radiation detector, for instance a wafer pyrometer, that measures the electromagnetic radiation coming from the wafer inside a field of vision that is defined by an optical device, for instance by a field stop shield or restrictor, that in general is a circular apertured plate. The wafer is heated by the electromagnetic radiation (largely thermal or infrared radiation) from heat sources, in particular from rod lamps that produce longitudinal virtual images on the wafer. For instance, at wafer temperatures greater than about 600° C., a wafer made of silicon acts like a mirror with reflectivity of approximately 30%, so that the mirroring property of the wafer produces virtual images of the rod lamps or heating device. The following is a simplified discussion of virtual images on the wafer or substrate or object.
During the temperature measurement, a differentiation is made essentially between systems heated on one side and systems heated on two sides. Systems heated on one side heat the wafer largely from only one side. In contrast, the temperature is measured on the other side, for instance by means of a wafer pyrometer. This determines a radiation that is largely unaffected by the lamp radiation and that is emitted by the wafer or a substrate, by means of which the substrate temperature is calculated.
FIG. 10 illustrates a system heated on one side. The substrate 6 is heated by a bank of lamps L arranged on one side of the substrate 6. The radiation emitted by the object is measured by a wafer pyrometer 8 that is arranged on the side opposite the bank of lamps.
In the one-sided heating systems it is disadvantageous that the speed at which the substrate is heated is limited due to the one-sided heating, whereby in general additional undesired temperature gradients caused by structures on the substrate surface occur within the substrate, in particular when the structures are formed or are present on the side of the substrate that faces the heat source. Furthermore, as a rule the chamber in which the substrate is processed is highly reflective in systems with one-sided heating. This highly reflective chamber limits the rate at which the substrate cools, which is disadvantageous in many processes. An additional disadvantage is that deposits such as condensation can occur when chamber walls are highly reflective, which changes the reflectivity of the walls, causing a temperature drift.
The aforesaid disadvantages can be substantially reduced, and to some extent avoided altogether, in a two-sided heating system such as that described, for instance, in DE 44 37 361, because in two-sided heating systems the substrate is heated from above and from below and therefore in general there is no need for a highly reflective chamber. Furthermore, greater heating speed can be achieved due to the heating on both sides. Since the substrate is also heated from the back side, which in general has no structures, the aforesaid temperature inhomegeneities caused by structures on the substrate surface can be substantially reduced. However, in contrast to the one-sided heating system, when there is two-sided heating the radiation measured by the wafer pyrometer is overlaid with an interfering radiation coming from the lamps due to the reflective properties of the substrate. The light reflected on the substrate and coming from the lamps, and the virtual lamp images resulting therefrom, appear more or less diffuse for the wafer pyrometer depending on the roughness of the substrate surface.
FIG. 11 illustrates a two-sided heating system that includes banks of lamps L1 and L2 on both sides of the substrate 6. Also shown are the virtual images V1 of the bank of lamps L1 occurring on the substrate 6 due to reflection. The banks of lamps L1, L2 can be arranged such that their virtual images cover those of the other bank of lamps. As can be seen in FIG. 11, the wafer pyrometer, within a field of vision, measures both the radiation Iw emitted from the wafer and a part of the lamp radiation Iiri determined by the reflecting properties of the substrate, whereby Ii is the lamp intensity of the ith lamp of the bank of lamps L1 and ri is an effective reflection coefficient of the substrate associated with lamp i.
If the substrate is made of silicon, when temperatures are less than 600° C. the overlay with the interfering radiation occurs both in one-sided heating systems and in two-sided heating systems, since silicon is transparent for infrared radiation in this temperature range, and the wafer pyrometer thus also detects a lamp radiation transmitted through the substrate.
The wafer pyrometer thus detects a radiation coming from the lamps, transmitted through the wafer, and reflected on the wafer, as well as a radiation emitted by the wafer, whereby the portion of the individual components depends on the coating of the substrate, the substrate thickness, and/or the substrate temperature. In order that the transmitted and reflected intensity of the lamps and their virtual images do not cause a false measurement result of the pyrometer, a part of the heat radiation of the lamps can be forwarded via a plurality of fan-like channels to a lamp pyrometer. The intensity measured in this manner can be used for correcting the intensity measured by the wafer pyrometer. The lamp pyrometer is inserted upstream of an imaging means, preferably a cylindrical lens that largely restricts the field of vision of the lamp pyrometer to a rectangle. The virtual images of the lamps move relative to the limits of the field of vision of the wafer pyrometer due to the vibrations that occur during the thermal processing procedure and due to thermally caused deformations and tilting of the wafer, so that changes occur in the intensity of the heat radiation measured by the wafer pyrometer. In particular this skews the amount of lamp radiation by reflection, which results in an error in the temperature measurement. If, for instance, during the measurement of the heat radiation with the wafer pyrometer, an apertured plate is used that restricts the field of vision between the wafer and the wafer pyrometer, fluctuations in intensity occur due to the round, continuous edge of the limited field of vision of the wafer pyrometer. This skews the measurement values for the temperature of the wafer surface.
In the RTP systems cited above, the heating apparatus generally includes a plurality of heating elements, for instance in the form of rod lamps, so that the electromagnetic radiation of each heating element can be individually adjusted by means of a suitable control apparatus. Not only does the option for the control result in numerous advantages in terms of temperature homogeneity across the wafer surface and flexibility with regard to the heating process, it also results in disadvantages for determining the temperature of the substrate or wafer, in particular when conventional wafer and lamp pyrometers are used. Thus, as described above, elements of the pyrometer, or more generally of the temperature sensors, that restrict the field of vision can have a negative effect on temperature measuring accuracy, especially when the intensities of the wafer and lamp pyrometers are compared for measuring the temperature in order, for instance, to correct the effect of the reflection of the lamp radiation on the substrate surface. For example, the vibrations of the substrate cited above, for instance, but also possible changes in intensity of individual heating elements in the heating apparatus, can interfere with the measurement result, in particular when the heating apparatus does not radiate uniformly in space.
Known from DE 41 14 367 A1 is a pyrometer for contactless temperature measurement of running measurement objects in which a cylindrical lens is provided for bundling the radiation coming from the measurement object.
Publications JP 5-187922 (A) in Patent Abstract of Japan, Sect. P, Vol. 17 (1993), No. 609 (P-1640) and DE-OS 21 50 963 indicate and describe contactless measurement of temperatures of an object, whereby a rectangular shield is provided between an optical member and an element that receives the radiation.
U.S. Pat. No. 5,061,084 indicates and describes an RTP system in which two pyrometers are provided, which system measures the radiation emitted by the object to be measured and the environment and the radiation emitted by the environment alone.
WO 94/00744 A1 indicates and describes an RTP system in which a radiation measurement device measures the radiation emitted by the wafer to determine its temperature, whereby one additional radiation measuring device is provided that measures the radiation emitted by the lamps.
U.S. Pat. No. 5,841,110 describes an RTP system in which two pyrometers are provided for measuring the wafer temperature and the ambient temperature or lamp temperature.
The object of the invention is to suggest and provide a method and an apparatus for measuring the temperature of substrates, with which method and/or apparatus it is possible to correctly and simply determine the substrate temperature, even when the substrate vibrates or tilts.